Earthworm Soil Avoidance Bioassay (2D)

Soil pollution — pesticides, heavy metals and petroleum products leaching from farmland, industrial sites and spills — is routinely screened with a cheap, standardized biological test rather than a lab assay alone: put earthworms in a chamber where one half is clean and the other is spiked with the suspect soil, and see which half they choose. This simulator runs a top-down 2D version of the ISO 17512-1 earthworm avoidance test: pick a contaminant (a heavy metal, an organophosphate pesticide, or diesel-range petroleum hydrocarbons), set its concentration relative to that compound's own avoidance EC50, and tune soil moisture, which raises contaminant bioavailability. Twenty worms follow a correlated random walk with a concentration-driven repulsion term, migrating out of the toxic half in real time while live readouts and a running strip chart track the control/test worm split, the standard avoidance-percentage formula A% = ((C−T)/N)×100, and the ISO classification the soil earns once the 48-hour test clock runs out.